The present invention relates to a bearing device for supporting a rotary shaft and a method of manufacturing a felt member used for the bearing device.
In some bearing devices, a sliding bearing and an annular felt ring are used to support a rotary shaft in the sliding bearing. The sliding bearing is made of a porous sintered alloy, and the felt ring is generally made of wool or polyester fibers. Lubricant oil is filled in the pores of the alloy and the felt. A cylindrical sliding bearing is held in position in a yoke of a motor. The felt ring is fit around the sliding bearing at the inside of the yoke. In this type of bearing device, the lubricant oil is allowed to move between the bearing and the felt ring.
The diameter of wool fibers varies between 10-70 micrometers (xcexcm). If wool fuzz are scattered from the wool felt and affixed between the sliding bearing and the rotary shaft, unacceptable noise sound is generated at the sliding surface during rotation of the rotary shaft. This may occur even after a motor is checked in a production process, and lowers the reliability of the checking.
Further, during rotation of the rotary shaft, heat is generated due to friction between the rotary shaft and the sliding bearing. The lubricant oil in the sliding bearing expands and its viscosity is lowered. Thus, the lubricant oil spills out from the sliding bearing. The lubricant oil spilled out from the radially inner side enables smooth rotation of the rotary shaft, while the lubricant oil spilled out from the radially outer side is absorbed and reserved in the felt ring.
The lubricant oil excessively spills out from the sliding bearing, when the sliding bearing is excessively heated due to rotations of the rotary shaft at high speeds for a long period of time. In this instance, the felt ring made of wool or polyester fibers becomes incapable of absorbing all the spilled lubricant oil therein. As a result, the amount of lubricant oil reserved in the sliding bearing decreases, resulting in burn-out of the sliding bearing in a short period. The lubricant oil spilled out but not absorbed in the felt ring scatters and affixes to surrounding parts. In the case of an electric motor, the scattering oil affixes to a commutator of the motor, causing clogging of the commutator or unusual noise sound during sliding of brushes on the commutator.
It is proposed to form blocking surfaces at predetermined locations for restricting the lubricant oil from spilling out too much from the sliding bearing. However, this blocking surfaces require special machining process and counteracts to required spilling of the lubricant oil.
It is therefore an object of the present invention to provide a bearing device and a method of manufacturing a felt ring for such a bearing device, which are capable of reducing unacceptable noise sound.
It is another object of the present invention to provide a bearing device, which is capable of reducing lubricant oil scattering outside.
According to the present invention, a bearing device for a rotary shaft is comprised of a porous sliding bearing and a felt ring fit around the sliding bearing, so that lubricant oil filled in the sliding bearing is absorbed in and returned from the felt ring, respectively. The felt ring is made of needle-punching polypropylene fibers of 0.4-20 micrometers in diameter. Preferably, the fibers are long-staple shape. The felt ring is manufactured by shaping the polypropylene fibers into a felt sheet by needle-punching, heat-treating the felt sheet to eliminate fuzz from the sheet surfaces, and punching the felt sheet in a ring shape. The sliding bearing has a plurality of grooves on its outer peripheral surface with which the felt ring contacts. Each groove is formed to extend in a horizontal direction to restrict the lubricant oil from flowing downward.